It is a known art to remotely control the motion of a crawler-type travelling body by using a remote controller (base device). A crawler-type travelling body is provided with a video camera. Image signals from the video camera are transmitted to a remote controller. An operator operates the remote controller while monitoring the motion of the crawler-type travelling body with a display monitor that accompanies the remote controller. Remote control signals from the remote controller are transmitted to the crawler-type travelling body to make the crawler-type travelling body turn or move forward, backward, or otherwise.
Systems for transmitting the image signals and the remote control signals include a wireless system and a wired system. A wired system is usually adopted when a crawler-type travelling body is used in a place where radio signals are not easily received such as in a building with winding passages and under the water. In the wired system, a crawler-type travelling body and a remote controller are connected with a long cable. Signal transmission wires are included in the cable. Feeder wires as power lines may also be included in the cable as necessary.
A robot for rescue operation or exploration may work in a site inside a building. Sometimes, an operator has to control a controller at a place distanced from the site by 100 meters or more, sometimes as far as 1000 meters, due to poisons, radiation, explosion risk and other risks that prevent him from getting closer to the site. Wired crawler-type travelling bodies are predominantly adopted for such robots.
In the wired crawler-type travelling body mentioned above, a reel for winding a cable therearound may be disposed in a base station where an operator is stationed, or may be disposed in the crawler-type travelling body.
In a case where a reel is disposed in a base station, when a crawler-type travelling body heads for a site a long distance away, it is required that the crawler-type travelling body unreel a cable from the reel in the base station and move drawing the long cable. This may cause too much load to the crawler-type travelling body.
To avoid such a situation, it is appropriate to dispose a reel on a crawler-type travelling body when a base station is a long distance away from a site. In this case, a cable is unreeled as the crawler-type travelling body is moved, and therefore, the load may be limited. It is preferable that a power line that tends to be heavy is not included in the cable but only a signal transmission wire that is thin, light-weight and strong is included in the cable.
However, when a reel is disposed on a crawler-type travelling body as mentioned above, a thin and long cable may be would around the reel. This may lead to a problem that the cable may become slack and hook onto a part of the crawler-type travelling body or the cable may get tangled, becoming unable to transmit signals, and as a result, making the crawler-type travelling body immovable.
Patent Document 1 to be identified later discloses a reel device disposed on a crawler-type travelling body. The reel device includes a reel around which a cable is wound, a motor connected to the reel and a rotation sensor that detects rotation of the reel.
In Patent Document 1, the motor is controlled by a motor controller basically as follows. When the crawler-type travelling body is moved in a direction (forward) away from the remote controller (base station) and the rotation of the reel in an unreeling direction is detected by the rotation sensor, the motor is made free, allowing the cable to be smoothly unreeled from the reel device, thereby preventing the cable from becoming too tense and from providing resistance against the forward movement of the crawler-type travelling body.
When the crawler-type travelling body is moved in a direction (backward) toward the remote controller, the motor is activated to reel the cable onto the reel, thereby preventing the cable from becoming slack.
The basic control as mentioned above alone may cause inconvenience. For example, when the crawler-type travelling body is moving forward, the motor is made free and the cable is allowed to unreel. In this condition, if the crawler-type travelling body is stopped suddenly, the reel will keep rotating due to the inertia, causing the cable to be unreeled more than necessary and to become slack.
To solve this problem, Patent Document 1 discloses an acceleration sensor that detects acceleration in a front-rear direction disposed in a crawler-type travelling body. When the crawler-type travelling body is stopped suddenly while moving forward as mentioned above, the motor is activated to rotate the reel in a reeling direction to reel the cable in response to the acceleration in a backward direction detected by the acceleration sensor.